In United Kingdom patent specification No. 620,720, accepted Mar. 29, 1949, to Hudson, there is described a plastic whistle formed of two basic parts. The first part includes a main body which includes a channeled throat merging into an internal cavity and both opening to one side of the body. The opening is closed by a closure or cover part which is adhered to the body by means of adhesive or the like to close the open side of the body and captivate a ball or the like within the cavity. While the structure performs relatively well as a whistle, it is subject to a number of substantial defects. Over a period of time, the adhesive may age and weaken to the point where the cover may disassociate from the body, thereby rendering the whistle useless.
Additionally, if care is not taken to insure that adhesive is present along the entire interface of the cover and body, leakage paths for air channeled into the whistle through the throat exist and air leaving the whistle via such leakage paths is not effective in producing the desired sound. Consequently, the efficiency of the whistle in converting a stream of air under pressure into sound is lessened.
Finally, since the air inlet opening in the throat of the body is not particularly strong in the area adjacent to the cover, a clamping force on the mouthpiece of the whistle exerted thereon by the teeth of the user will tend to cause the mouthpiece to collapse and if the adhesive fractures, collapse will in fact occur. Thus, the whistle can be rendered useless.
In U.S. Pat. No. 2,113,396, issued on Apr. 5, 1938, to Butterfield, there is also described a plastic whistle made in two parts. In one embodiment thereof, the whistle is made with a major body and a lesser cover in a fashion somewhat similar to that disclosed in the Hudson British patent specification identified above. In this embodiment, the two parts are held together by a rivet or the like with the cover being received in a recess provided with a shoulder in the main body.
Because the cover is received in a recess in the main body, it provides support for the throat adjacent the mouthpiece against collapse due to tooth pressure. And the use of a rivet for securing the parts together does eliminate the problem of aging adhesive. However, the entire interface of the cover and the body is not sealed completely effectively with the consequence that leakage around the entire interface of the body and the cover can occur, again, lowering the efficiency of the process of converting a moving air stream to sound provided by the whistle. Moreover, because the cover must be inserted in a recess, assembly is made more difficult. The appearance of the exterior of the whistle may be adversely affected to the extent that the thickness of the cover deviates from the depth of the recess in which it is received.